The invention relates to a gasket, particularly a cylinder head gasket, as well as to a process for the production thereof.
Gaskets and in particular cylinder head gaskets, require at the sealing point a specific contact pressure to enable then to fulfil their function. In the case of larger sealing surfaces, such as between a cylinder head and a cylinder block of internal combustion engines, this contact pressure is produced with the aid of screws, the forces having to be distributed in a planned manner over the surface.
On reaching an adequate contact pressure or sealing force between two screws on the gasket, there is a certain deflection or sagging of the surfaces to be sealed. In order to obtain a sealing action in spite of these different deflections of the facing sealing surfaces, use is conventionally made of soft gaskets or packings. The latter undergo thickness deformation on assembly or installation, so that there is a function-ensuring pressure distribution.
A gasket of the present type is known from German Published Application 19 23 482. In the unassembled state, circular sealing combs projecting from the sealing plane are arranged concentrically round the combustion chamber openings and alternating therewith there are depressions in the sealing plane. The height of the sealing combs is adapted to the screw spacings. As a result of this measure, after fitting between the sealing surfaces, i.e. after fixing the gasket, as a result of the increased contact pressure acting on the sealing combs there is a material flow from said combs to the depressions, so that the sealing comb which is to be almost completely recovered adapts to the precise contour of the sealing surface which is never precisely planar as a result of distortion. However, there is a risk of the sealing surfaces being damaged by these combs.
In addition, German Published Application 39 22 284 discloses a cylinder head packing essentially made from soft material, in which there are at least two juxtaposed passage openings separated by a web. On the edges or rims of the passage openings, the soft material is provided with metallic, circular, cross-sectionally U-shaped combustion chamber borders. On the web is placed a metal reinforcement, which at least on one side has a predetermined curvature for compensating the deflection of the sealing surfaces. However, there is no accurate, individual adaptation of the curvature of the reinforcing insert to the deflection line of the sealing surface.
German Published Application 22 28 155 discloses soft gaskets with cross-sectionally adapting sheet metal plates on the web between two passage openings. However, this only leads to a very approximate adaptation to the shape of the surfaces to be sealed, because the cross-sectional change occurs in relatively large steps. It is particularly disadvantage with said stepwise thickness adaptation, that it is not possible along a closed sealing line without leakage points.
It is considered disadvantageous in such soft gaskets, that initially they must be deformed in the assembly state under the same screw forces under which they must subsequently function in "stable" manner in the operating state without any further deformation. A further disadvantage is the complicated construction of the gasket solely for the purpose of obtaining the necessary contact pressure distribution by an engine-corresponding thickness distribution over the surface during the assembly phase.
Another problem is the precise maintenance of the assembly thickness, because there are relatively significant fluctuations in the soft material thickness and this is also additionally dependent on the deformability of the sealing material and the level of the screw forces. It is also problematical that a considerable proportion of the material components of a soft gasket is not recyclable.
Moreover metal gaskets have long been in use, which are made from a relatively soft metal. However, it is considered disadvantageous in connection therewith that the local deformation require higher forces on assembly to obtain a smaller thickness and consequently no planned contact pressure is possible. During assembly or fitting, such gaskets cannot be supplied with the necessary contact pressure at precisely the desired points. No planned contact pressure can be obtained with metal gaskets that are deformable during installation. Such gaskets can only be used in those cases where high screw forces are available. Conversely this precludes the use for lightweight constructions.
In addition, metal gaskets are often provided with stiffening corrugations, which are height-deformed during installation and are intended to locally give the gasket an improved adaptation. However, this leads to the disadvantage that, at the points with the maximum assembly thickness, a bearing action is only exerted by the corrugation, which as a result of thermal component deformation, like a soft gasket, can be further deformed in operation.